The Earth Science Picture of the Day (EPOD) highlights the diverse processes and phenomena which shape our planet and our lives. EPOD will collect and archive photos, imagery, graphics, and artwork with short explanatory captions and links exemplifying features within the Earth system. The community is invited to contribute digital imagery, short captions and relevant links.

How Old is the Earth?

It is generally considered that the Earth is about four and a half billion years old, a long time in other words, but how long is that really? How can all that time be represented graphically so as to get an idea of the expanse? I happened to see a surveyor out in the street in front of my house (in Seattle, Washington) the other day and struck up a conversation with him in which he told me exactly how far it was to the corner of the block. Since I’ve been around the block once or twice I wondered if I could describe the age of the Earth in trips around the block. It was easy enough to calculate from the figures he gave me how far it is around the block, but I had no interest in making 4,550,000,000 trips so it became a question of scale. According to the survey it is 50,279.59 centimeters around the block. Let’s round that to 500,000 millimeters. So if one year equals one millimeter it would be 9,100 trips around the block. Not something I’m likely to do any time soon. But we can get that down to just over nine trips if we make 1 mm equal 1,000 years! In that scale, assuming my front door is today, the earliest humanoids would be living about 13 feet (about 4 m) from my front door.